U.S. Pat. No. 4,177,290 describes modafinil in racemic form, also known as (±) 2-(benzhydrylsulphinyl)acetamide or (±) 2-[(di-phenylmethyl)sulphinyl]acetamide, as a compound having properties of stimulating the central nervous system.
U.S. Pat. No. 4,927,855 describes the two optical enantiomers of modafinil. More particularly it describes the laevorotatory enantiomer and its use as an antidepressant or stimulant agent in the treatment of hypersomnia and disorders associated with Alzheimer's disease. The process for the preparation of the two optical enantiomers of modafinil from (±) modafinil acid or (±)-benzhydrylsulphinylacetic acid described in this document is illustrated in the following synthesis diagram:

This process comprises carrying out resolution of the optical enantiomers of (±) modafinil acid in a first stage via the formation of diastereoisomers with the optically active agent α-methylbenzylamine.
The (−)-α-methylbenzylamine-(−)-benzhydrylsulphinyl acetate is then converted to (−)-benzhydrylsulphinylacetic acid by acid hydrolysis. The latter is esterified in the presence of dimethyl sulphate and then converted to amide in the presence of ammonia (gas). The (−) or l (laevorotatory) enantiomer of modafinil is obtained through this process with an overall yield of 5.7% in relation to the (±) modafinil acid, calculated on the basis of the yields corresponding to each stage.